1. Field of the Invention
This invention relates generally to the field of fiber optic signal transmission coupling devices used to interconnect a pair of terminated optical fibers for light transmission therethrough, and more particularly to an adjustable attenuation adapter for fiber optic connectors for varying the air gap between the ends of the aligned terminated optical fibers in a controlled manner to provide variable optical attenuation to a transmitted signal.
2. Description of the Related Art
Attenuators are used in fiber optic systems to reduce the optical power received by the photodetector to a level that is within the dynamic range of the optical receiver. The light intensity control of laser diodes and LEDs is limited in dynamic range and can result in an undesired change in radiation pattern, modal structure and central wavelength. Light intensity control at the transmitter has the additional disadvantage of requiring either remote power monitoring at the destination central office receiver or loop-back. Therefore, for interoffice transmission applications, attenuators are normally employed at the destination central office. immediately in front the receiver.
Attenuators of fixed type are often adequate to adjust the received power level to within the required range. Attenuators of variable type are useful for periodic adjustment of received power should the link loss output increase or decrease during the life of the transmission system. Increased link loss may be caused by degradation of the fiber, splices, or optical connectors. In additions, variable attenuators are also important for optical measurements, such as BER as a function of received power, which are important for characterizing the performance of transmission systems.
There are mainly three different types of designs of optical-fiber attenuators: mechanical attenuators, see A. Benner, H. M. Presby. and N. Amitay, xe2x80x9cLow-reflection in-line variable attenuator utilizing optical fiber taper,xe2x80x9d J. of Lightwave Technology, Vol. 8, No. 1, pp. 7-10, January, 1990, laser diode attenuators, see N. Kashima, xe2x80x9cA new approach to an optical attenuator for a time compression multiplex system using a laser diode as both transmitter and receiverxe2x80x9d, J. of Lightwave Technology, Vol. 9, No. 8, pp. 987-990, August, 1991, and fused attenuators, see e.g. M. Cork, xe2x80x9cPassive fiber optic components,xe2x80x9d Short Course Notes, OFC""91, San Diego, p. 63, February, 1991.
In the prior art, there exist a variety of structures for introducing variable attenuation. Some structures include a wheel having a plurality of neutral density filters which are selectively introduced into the gap. Others employ a movably mounted reflective surface. Still other methods employ heating and twisting of the fibers. U.S. Pat. No. 4,145,110 granted Mar. 20, 1979 to Otti Szentesi, discloses a relatively low-cost device to accomplish this purpose in which a connecting structure firmly holds one terminated fiber in relatively fixed position, while varying the other fiber using a threaded nut toward and away from the fixed fiber to vary the distance therebetween. While not without utility, the construction is rather large in overall size, precluding use of the same in an area where space limitations are critical, and the construction employs parts which are not easily manufactured using mass production techniques, such as die castings.
U.S. Pat. No. 5,187,768 granted Feb. 16, 1993 to Ott, et al., discloses a fiber optic connector having an adjustable element providing for optical signal attenuation. The connector includes a pair of plug connector elements maintained in axially aligned relation upon engagement with a medially positioned adapter element. One of the plug connector elements incorporates the adjustable element, movement of which varies the gap existing between the aligned ends of the optical fibers without relative rotation between the end surfaces of the fibers. However, the construction is difficult to adjust an desired attenuation and employs parts which are not easily manufactured.
It is a primary object of the present invention to provide an adjustable attenuation adapter for fiber optic connector for easily varying the air gap between the ends of the aligned terminated optical fibers to provide variable optical attenuation to a transmitted signal.
It is another object of the present invention to provide an adjustable attenuation adapter for fiber optic connector which is rather compact overall so as to be employed in an area where space limitations are critical.
It is a further object of the present invention to provide an adjustable attenuation adapter for fiber optic connector which is easy to adjust an desired attenuation.
According to the present invention, the adjustable attenuation adapter mainly comprises a fixing body, a moving body, a fixing plate, an adjusting knob, and a fixing knob. The fixing body includes a plate, a bore centrally disposed in the plate, and a threaded connecting member extending outwardly from the bore. The moving body includes a cylindrical body extending between a larger end and a smaller end having an orificed end wall. The cylindrical body has a threaded outer surface to be threadedly driven by an inner roller and the larger end has a threaded outer surface to be threadedly engaged with a plug connector element. An alignment sleeve serves to engage the ferrule on each of the first and second plug elements and maintain axial alignment therebetween. The alignment sleeve is positioned within the moving body and is enclosed by a sleeve cap having an orificed end wall. The fixing plate includes a plate and a bore centrally disposed therethrough. The adjusting knob is sandwiched between the fixing body and the fixing plate. The inner roller has an outer surface with gear teeth to be driven by the gear body of the adjusting knob and an inner threaded surface for driving the threaded outer surface of the cylindrical body of the moving body. The inner roller is sandwiched between the fixing body and the fixing plate. A fixing knob controls the position of the detent with respect to the inner roller.
The adjustable attenuation adapter serves to interconnect the FC-type plug elements of fiber optic connectors. When the ferrules and of the first and second plug elements are in substantially abutted condition, minimum optical attenuation is obtained. Where greater attenuation is required, the fixing knob is rotated in a manner that the fixing knob does not press the detnet against the inner roller. Then, the adjusting knob is rotated such that the gear body drives the gear teeth of the inner roller to rotate. The rotation of the inner roller causes the axial displacement of the moving body with respect to the fixing body and the fixing plate. When the moving body is moved away from the fixing body, the ferrule of the second plug element is also moved away from the ferrule of the first plug element and thus an air gap exists between the two ferrules and of the first and second plug elements and, which results in greater optical attenuation.
Briefly stated, the invention contemplates the provision of an improved construction of the type described in which the above-mentioned disadvantages have been substantially eliminated. Adjustment is performed by manually rotating the adjusting knob forming a part of the attenuator which results in the longitudinal displacement of an optical fiber in one of the plug connectors with respect to the other, without, in any manner, disturbing the relative angular relation of the optical fibers, and without, in any manner, effecting any lateral displacement of the axis of either optical fiber.